The present invention relates to a method of ultrasonically welding a first thermoplastic member within an opening in a second thermoplastic member and to fabricating a microwave oven thermometer employing such method.
Various products may include two or more plastic elements which are to be permanently joined or interconnected. Such plastic elements can be interconnected by the use of a suitable adhesive or, by appropriate selection of material and processes, directly integrally bonded or welded to each other. For thermoplastic elements, ultrasonic welding is often employed wherein the members are mounted in engagement and coupled to an ultrasonic welding electrode or horn. In accordance with well-known processes, the horn, in turn is coupled to an electroacoustical energy source to establish high frequency vibratory motion of the coupled elements. The high frequency vibration results in the softening of the thermoplastic material, and a welding of the two elements upon terminating of the vibration and hardening of the softened or molten plastic materials. Generally the parts or elements are carefully formed and fitted in order to produce high strength joints. This, of course, requires careful and costly manufacturing and assembly processes for mass produced and particularly low cost items, it would be desirable to eliminate the necessity for expensive forming of the component parts and permit component manufacture with relatively large tolerances.
For example, microwave oven thermometers generally include a glass thermometer stapled to a metal support. In an operating oven the microwave energy would generally be reflected by the metal support and arcing with the magnetron tube may result. The possible damage to the tube which would result from the arcing prevents insertion of the thermometer during oven operation. In use therefore, the operator must turn off the oven, insert the thermometer and then remove the thermometer before again turning on the oven. Certain plastics such as polysulfone are not destroyed or adversely effected by microwave energy and may support a glass thermometer within an operating microwave oven. The glass tubing generally is formed with a relatively wide tolerance on the order of 0.037 inches. In attaching the glass tube to a plastic support, the structure and process should accomodate such wide tolerances.